Just tested my Alfa AWUS051NH v.2 on Kali: monitor mode & packet injection are working after applying the latest updates. For reference, here is the output of uname -a && cat /etc/*-release && cat /proc/version on my box.
Linux kali 4.12.0-kali1-amd64 #1 SMP Debian 4.12.6-1kali6 (2017-08-30) x86_64 GNU/Linux
DISTRIB_ID=Kali
DISTRIB_RELEASE=kali-rolling
DISTRIB_CODENAME=kali-rolling
DISTRIB_DESCRIPTION="Kali GNU/Linux Rolling"
PRETTY_NAME="Kali GNU/Linux Rolling"
NAME="Kali GNU/Linux"
ID=kali
VERSION="2017.2"
VERSION_ID="2017.2"
ID_LIKE=debian
ANSI_COLOR="1;31"
HOME_URL="http://www.kali.org/"
SUPPORT_URL="http://forums.kali.org/"
BUG_REPORT_URL="http://bugs.kali.org/"
Linux version 4.12.0-kali1-amd64 (
[email protected]) (gcc version 6.4.0 20170820 (Debian 6.4.0-4) ) #1 SMP Debian 4.12.6-1kali6 (2017-08-30)